Grabbed a cheap 135 Mamiya TLR lens on eBay tonight - we'll see what that does in a few days. I have the 127/4.7 Ektar and that does indeed cover 4x5, at least any closer than infinity. Checked a 101 Raptar which seems to cover too well also. Will test other options as time allows. Even 6x9 lenses would fill the narrow dimension of the 4x5 frame though, I think.
Thanks for suggestions.